1. Field of the Invention
The present invention relates to an FM receiver capable of preventing adjacent interference and, more particularly to an FM receiver designed for use in vehicles.
2. Description of the Related Art
As is known in the art, adjacent waves often causes interference in FM receivers, especially in vehicle-mounted FM receivers. The method hitherto used to eliminate the adjacent interference occurring in an FM receiver was to switch the frequency band of the ceramic filter or the like incorporated in the FM receiver, which determines the IF (Intermediate Frequency) band, from a broad one to a narrow one. At present, the IF-band switching is performed in accordance with the data by output by a system which is other than the system for receiving desired signals and which is designed to prevent adjacent interference. It is expected that most conventional FM receivers will be soon replaced by less expensive self-detecting FM receivers in which the system for receiving desired signals detects and controls adjacent interference.
In the conventional FM receiver capable of preventing adjacent interference, adjacent interference is prevented in the following manner. The + detuning adjacent interference detector and the - detuning adjacent interference detector, both incorporated in the FM receiver, detect the intermediate frequencies derived from the desired station's frequency. The intermediate frequencies are added, thereby finding a adjacent interfering signal. The adjacent interfering signal is removed.
The conventional FM receiver has a complex structure.